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Gerasimos K. Politis 《Ocean Engineering》2011,38(4):699-711
We solve the problem of unsteady potential flow around a system of arbitrarily moving rigid or flexible, lifting or non-lifting bodies, in an infinite fluid free of distributed vorticity. For the solution we use a time stepping algorithm and a potential based formulation of the corresponding free BVP. Nonlinear free shear layer dynamics are included in our modeling. This is a major innovation in treating complex unsteady propulsion problems since no simplifying assumptions (like that of a helicoidal wake) are used regarding the wake model. Bilinear quadrilateral elements are used to describe body and shear layer geometry at each time t. Three types of Kutta conditions can be alternatively applied for the determination of the shed vorticity from lifting bodies. The theoretical and numerical aspects of the method are presented followed by a number of applications, elucidating the qualitative and quantitative physical characteristics of a number of complex unsteady propulsion problems. 相似文献
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A coupled-mode model is developed for treating the wave–current–seabed interaction problem, with application to wave scattering by non-homogeneous, steady current over general bottom topography. The vertical distribution of the scattered wave potential is represented by a series of local vertical modes containing the propagating mode and all evanescent modes, plus additional terms accounting for the satisfaction of the free-surface and bottom boundary conditions. Using the above representation, in conjunction with unconstrained variational principle, an improved coupled system of differential equations on the horizontal plane, with respect to the modal amplitudes, is derived. In the case of small-amplitude waves, a linearised version of the above coupled-mode system is obtained, generalizing previous results by Athanassoulis and Belibassakis [J Fluid Mech 1999;389:275–301] for the propagation of small-amplitude water waves over variable bathymetry regions. Keeping only the propagating mode in the vertical expansion of the wave potential, the present system reduces to an one-equation model, that is shown to be compatible with mild-slope model concerning wave–current interaction over slowly varying topography, and in the case of no current it exactly reduces to the modified mild-slope equation. The present coupled-mode system is discretized on the horizontal plane by using second-order finite differences and numerically solved by iterations. Results are presented for various representative test cases demonstrating the usefulness of the model, as well as the importance of the first evanescent modes and the additional sloping-bottom mode when the bottom slope is not negligible. The analytical structure of the present model facilitates its extension to fully non-linear waves, and to wave scattering by currents with more general structure. 相似文献
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A non-linear coupled-mode system of horizontal equations is presented, modelling the evolution of nonlinear water waves in finite depth over a general bottom topography. The vertical structure of the wave field is represented by means of a local-mode series expansion of the wave potential. This series contains the usual propagating and evanescent modes, plus two additional terms, the free-surface mode and the sloping-bottom mode, enabling to consistently treat the non-vertical end-conditions at the free-surface and the bottom boundaries. The present coupled-mode system fully accounts for the effects of non-linearity and dispersion, and the local-mode series exhibits fast convergence. Thus, a small number of modes (up to 5–6) are usually enough for precise numerical solution. In the present work, the coupled-mode system is applied to the numerical investigation of families of steady travelling wave solutions in constant depth, corresponding to a wide range of water depths, ranging from intermediate depth to shallow-water wave conditions, and its results are compared vs. Stokes and cnoidal wave theories, as well as with fully nonlinear Fourier methods. Furthermore, numerical results are presented for waves propagating over variable bathymetry regions and compared with nonlinear methods based on boundary integral formulation and experimental data, showing good agreement. 相似文献
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Christos Makris Panagiota Galiatsatou Konstantia Tolika Christina Anagnostopoulou Katerina Kombiadou Panayotis Prinos Kondylia Velikou Zacharias Kapelonis Elina Tragou Yannis Androulidakis Gerasimos Athanassoulis Christos Vagenas Ioannis Tegoulias Vassilis Baltikas Yannis Krestenitis Theodoros Gerostathis Kostantinos Belibassakis Eugen Rusu 《Ocean Dynamics》2016,66(12):1603-1635
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G. A. Athanassoulis K. A. Belibassakis Th.P. Gerostathis 《Journal of Atmospheric & Ocean Science》2002,8(2):201-217
In the present work, the Poseidon Nearshore Wave Model (PNWM) developed in the framework of the POSEIDON project 1 , and its application to the prediction of the wave conditions in nearshore/coastal regions of Greek seas is presented. The PNWM is based on a one-way energy coupling between a third-generation, phase-averaged, nearshore wave model and a local phase-resolving model, nested in the first model. The local wave model is supported by the consistent coupled-mode theory, based on an enhanced local-mode representation of the wave velocity field, which except for the propagating and the evanescent modes includes an additional mode, permitting the exact satisfaction of the sloping-bottom boundary condition, even in areas with locally steep bottom slope and large curvature. Thus, three-dimensional diffraction effects are fully treated in the local nested area. Numerical results are presented demonstrating the application of the PNWM to nearshore and coastal sites of the Greek seas. 相似文献
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A consistent coupled-mode model recently developed by Athanassoulis and Belibassakis [1], is generalized in 2+1 dimensions and applied to the diffraction of small-amplitude water waves from localized three-dimensional scatterers lying over a parallel-contour bathymetry. The wave field is decomposed into an incident field, carrying out the effects of the background bathymetry, and a diffraction field, with forcing restricted on the surface of the localized scatterer(s). The vertical distribution of the wave potential is represented by a uniformly convergent local-mode series containing, except of the ususal propagating and evanescent modes, an additional mode, accounting for the sloping bottom boundary condition. By applying a variational principle, the problem is reduced to a coupled-mode system of differential equations in the horizontal space. To treat the unbounded domain, the Berenger perfectly matched layer model is optimized and used as an absorbing boundary condition. Computed results are compared with other simpler models and verified against experimental data. The inclusion of the sloping-bottom mode in the representation substantially accelerates its convergence, and thus, a few modes are enough to obtain accurately the wave potential and velocity up to and including the boundaries, even in steep bathymetry regions. The present method provides high-quality information concerning the pressure and the tangential velocity at the bottom, useful for the study of oscillating bottom boundary layer, sea-bed movement and sediment transport studies. 相似文献
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Mauro Sclavo Luigi Cavaleri Stephen F. Barstow Gerassimos A. Athanassoulis 《Marine Ecology》2002,23(S1):361-369
Abstract. We describe a software system that allows even an inexperienced user to estimate the wave statistics at any location along the European coastal zone. The system is composed of a solid, well verified data set, a geographical tool, a modelling section and a statistical package. Their use is fully transparent to the user. 相似文献
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